JP5509128B2 - Image brightness automatic correction device and high-speed photographing device provided with the same - Google Patents

Description

  The present invention relates to a device for measuring a change in luminance of an illumination light source and automatically correcting the luminance of a photographed image based on the change in luminance in a photographing using a strobe light source in a high-speed photographing device, and a high-speed photographing provided with the device. Relates to the device.

  Conventionally, when photographing a high-speed phenomenon, a high-speed photographing device capable of photographing at a higher speed than a general imaging device is used. In high-speed shooting, since the exposure time per frame decreases in proportion to the shooting speed, the captured image becomes dark without sufficient illumination. For this reason, a strobe light source is often used in the case of ultra high-speed shooting where the shooting speed exceeds tens of thousands of fps (frames per second). However, as shown in FIG. 1, the strobe light source has a light emission characteristic that the luminance gradually increases from the start of light emission and gradually decreases when the maximum luminance is reached. Cannot illuminate. For example, if strobe lighting with a light emission time (a time that is half or more from the maximum luminance) is used, the light emission time corresponds to 100 frames when the shooting speed is 100,000 fps. The brightness of the subject illuminated by the flash light source changes every 100 frames.

Japanese Patent Publication No. 6-71319

  Originally, strobe lighting is used for photography, and the time change of strobe lighting is much shorter than the shutter speed, and all emitted light is used for one image. As shown in FIG. 2A, there is no problem even if there is a light emission characteristic.

  However, during high-speed shooting, depending on the shooting speed, the exposure time of one frame is sufficiently shorter than the light emission time. Therefore, as shown in FIG. It cannot be photographed in the same way as when using illumination with uniform brightness. As already disclosed in Japanese Patent Application Laid-Open No. H10-260, there is already one that detects a change in luminance from a video signal for each frame and automatically controls the exposure time using an electronic shutter function of a solid-state imaging device. In this case, the processing time may not be able to keep up. In addition, when the subject moves at high speed, motion blur may occur depending on the exposure time. However, if the exposure time is changed for each frame, the amount of motion blur changes accordingly. There is also the possibility of becoming natural.

  For this reason, until now, there have been many cases where the luminance change is accepted and the image is taken as it is.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an apparatus that automatically corrects the luminance level of an acquired image to an appropriate luminance level after image capturing in accordance with the luminance level fluctuation of a light source. And

  Of the inventions disclosed in this specification, the outline of typical ones will be briefly described as follows.

  (1) In the present invention, an average luminance value of each frame of a video shot with the first flash illumination is calculated, a correction coefficient of each frame is calculated from the average luminance value of each frame, and the first flash A calculation unit that generates corrected image data using the image data of each frame of the video shot with the second flash illumination after shooting with the illumination and the correction coefficient of each frame; and each of the calculation units calculated by the calculation unit It is an image luminance automatic correction apparatus including a correction coefficient recording unit that records a correction coefficient of a frame.

  (2) In the above (1), instead of calculating the correction coefficient from the image data of each frame of the video shot with the first flash illumination, the calculation unit performs shooting with the first flash illumination. The correction coefficient of each frame is calculated from the average luminance value of each frame of the video shot with the second flash illumination, and the image data of each frame of the video shot with the first flash illumination and the respective Corrected image data is generated using a frame correction coefficient.

  (3) In the above (1) or (2), the correction coefficient is a value proportional to [1 / average luminance value of each frame], and the calculation unit applies the correction coefficient to the image data of each frame. Multiply to generate corrected image data.

  (4) In the above (3), the calculation unit calculates an average luminance value of each frame and an average luminance value of all frames, and calculates the average luminance value of each frame from the average luminance value of each frame and the average luminance value of all frames. A correction coefficient is calculated, and the correction coefficient is [average luminance value of all frames / average luminance value of each frame].

  (5) In the above (1) to (4), the calculation unit calculates the average luminance value of each frame by averaging the luminance values of all the pixels of each frame.

  (6) A high-speed photographing device including the image brightness automatic correction device according to any one of (1) to (5).

  In high-speed shooting that requires flash illumination, the present invention measures the light emission characteristics of flash illumination in advance, and automatically corrects the image after shooting so that it can be taken using powerful illumination with constant brightness. It is an object of the present invention to provide an apparatus that makes it possible to obtain an image such as that performed.

It is a figure which shows the example of the light emission time characteristic of a strobe light source. It is a figure which shows the difference in the exposure time in the case of a photograph, and high speed photography. It is a figure which shows the image of the brightness | luminance correction of embodiment of this invention. It is a figure which shows the high-speed imaging device of the Example of this invention. It is a block diagram of the image brightness automatic adjustment device of the embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a diagram showing an image of luminance correction according to the embodiment of the present invention. FIG. 3A is a diagram showing a temporal change in the average luminance of each frame when photographing with strobe illumination emitted against a background without a subject, and FIG. 3B is photographed when there is a subject with strobe illumination. FIG. 3 (c) is a diagram showing a correction coefficient calculated from the time change of the luminance of the strobe illumination, and FIG. 3 (d) is as powerful as the strobe. It is a figure which shows the time change of the average brightness | luminance of each flame | frame when it image | photographs using the illumination supposing there exists uniform illumination with which light emission intensity does not change.

  Assume that an image obtained by causing a strobe to emit light against a background without a subject and photographing it at a high speed changes in luminance as shown in FIG. A plot of the correction coefficient calculated from this video versus time is the graph of FIG. That is, first, for example, when shooting with only a strobe light in a state where there is no subject, an image in which the brightness of each frame changes according to the luminance change as shown in FIG. Calculate (detect) the average luminance value of the screen of each frame from the video, obtain the average luminance value for all frames, calculate the correction coefficient for each frame from the average luminance value of each frame and the average luminance value of all frames. Record. The correction coefficient recorded in this way is the correction coefficient shown in FIG.

  Next, for example, when a subject moving at high speed is photographed using a strobe, an image having a luminance change as shown in FIG. 3B is obtained. This figure shows a state in which the brightness is temporarily increased due to reflection of the subject on the way. When the image data of each frame of the video is multiplied by the recorded correction coefficient, a video having a luminance change similar to the luminance change when shooting with uniform illumination as shown in FIG. 3D is output. be able to.

  As shown in FIG. 3D, the correction coefficient is calculated from the temporal change pattern of the illumination light obtained by the pre-photographing, and when the luminance level is low, the entire image is corrected to be brightened, and the luminance level has increased. On the other hand, by correcting so that the entire screen is darkened, it is possible to obtain an image as if the image was shot with a constant luminance despite shooting with strobe lighting with varying luminance.

  If the correction coefficient is inversely proportional to the average luminance value of each frame, it is possible to perform relative correction over the time of the illumination light on the image data obtained by photographing the subject. Further, if the correction coefficient is made proportional to the average luminance value of all frames, an image as if it was shot with a constant luminance illumination having the same brightness as the average luminance value of all frames can be obtained.

  Hereinafter, a high-speed imaging device and an image brightness automatic correction device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 4 shows a high-speed photographing apparatus according to an embodiment of the present invention. Reference numeral 1 denotes a high-speed photographing device, 2 denotes an image sensor, 3 denotes a memory, 4 denotes a control circuit, 5 denotes an image brightness automatic correction device, 6 denotes a subject, and 7 denotes a strobe lighting device.

  In FIG. 4, when photographing is performed using the strobe lighting device 7, in the high-speed photographing device 1, image data obtained by photographing the subject 6 is stored in the memory 3 from the imaging device 2 through the control circuit 4. In the first photographing, the image brightness automatic correction device 5 reads the data in the memory 3 and calculates the average brightness value of each frame and the average brightness value of all frames.

  FIG. 5 is a block diagram of the image brightness automatic correction apparatus. 5 is an image brightness automatic correction device, 51 is an image storage unit that stores an image for one frame, 52 is an average brightness value of each frame of an image shot with flash illumination, an average brightness value of all frames, and correction of each frame. A calculation unit that calculates a coefficient, and calculates corrected image data from a video from the image storage unit 51 and a correction coefficient obtained by shooting before shooting the video; and 53, a correction coefficient for each frame calculated by the calculation unit Is a correction coefficient recording unit for recording

  First, the background is photographed using a flash light source in the same manner as in actual photographing, the image data is fetched into the image storage unit 51 for each frame, and the luminance of all the pixels in the frame fetched by the calculation unit 52 is captured. The average value of is calculated. This is sequentially repeated over all frames, and the average of the luminance values of all the frames is obtained from the average luminance value of each frame. Then, a correction coefficient is calculated based on the average luminance value of each frame and the average luminance value of all frames, and the value is held in the correction coefficient recording unit 53. In the arithmetic unit 52, for example, the reciprocal of [the average luminance value of received frames / the average luminance value of all frames] is used as a correction coefficient, and the corrected data is created by multiplying the data of each frame to be photographed next. The correction coefficient is recorded in the correction coefficient recording unit 53. If the correction coefficients of each frame are arranged in time order, a graph as shown in FIG.

  In the subsequent shooting, the image data is read from the memory 3 in units of one frame, and the data automatically corrected for brightness using the correction coefficient recorded in the first shooting is written back to the memory 3.

  That is, in the second and subsequent photographing, the calculation unit 52 corrects and outputs the image data using the image data of one frame of the image storage unit 51 and the correction coefficient of the frame recorded in the correction coefficient recording unit 53. Repeat the above for the number of frames. As a result, the calculation unit 52 multiplies the image data from the image storage unit 51 (see FIG. 3B) and the correction coefficient recorded in the correction coefficient recording unit 53 (see FIG. 3C). An image (see FIG. 3 (d)) having a luminance change as if the image was shot using strong illumination with a constant luminance is output.

  The image storage unit 51 may be omitted by using the memory 3 of FIG.

  At the time of shooting, the flash illumination device 7 is caused to emit light by sending a signal from the outside. Further, in many cases, a trigger signal can be input to the high-speed imaging device 1, and the timing of imaging can be controlled by an external signal. Therefore, an external signal to be sent to the flash illumination device 7 can also be input to the camera, so Light emission and camera operation can be synchronized. As described above, by synchronizing the flash emission and the camera operation, it is possible to make the first shooting frame correspond to the second and subsequent shooting frames. Further, the frame at the first photographing may be associated with the frame at the second and subsequent photographing by another method.

  As described above, the embodiment of the present invention has been described in detail. However, the image brightness automatic correction apparatus according to the present invention calculates the average brightness value of each frame of the video shot with the first flash illumination, and calculates the average of each frame. A correction coefficient for each frame is calculated from the luminance value, and a corrected image is obtained using the image data of each frame of the video shot with the second flash illumination after the shooting with the first flash illumination and the correction coefficient of each frame. A calculation unit 52 that generates data and a correction coefficient recording unit 53 that records the correction coefficient of each frame calculated by the calculation unit 52 may be provided.

  If the number of frames to be taken is reduced by half, an image containing the subject is taken for the first time and stored in the memory 3, and then the second shooting is performed in the background without the subject, and the calculation unit 52 The correction coefficient of each frame may be obtained and stored in the correction coefficient recording unit 53, and then the luminance corrected video may be output. In this case, since the second shooting can be performed immediately after the first shooting, it is possible to deal with a case where it is difficult to obtain a correction value by flashing in advance, such as affecting the subject.

  The correction coefficient is a value proportional to [1 / average luminance value of each frame], and corrected image data may be created by multiplying the image data of each frame of the captured video by the correction coefficient.

  This correction coefficient can be [average luminance value of all frames / average luminance value of each frame].

  Further, the arithmetic unit 52 may calculate the average luminance value of each frame by averaging the luminance values of the pixels of each frame, and the average luminance value of all the frames may be calculated from the average luminance value of each frame.

  The high-speed photographing apparatus 1 according to the embodiment of the present invention only needs to include the above image luminance automatic correction apparatus. Alternatively, a signal to be sent to the flash illumination device 7 may be input to capture an image in synchronization with the light emission of the flash illumination device 7.

  As mentioned above, the invention made by the present inventor has been specifically described based on the above embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Of course.

DESCRIPTION OF SYMBOLS 1 ... High-speed imaging device, 2 ... Image sensor, 3 ... Memory, 4 ... Control circuit, 5 ... Image brightness automatic correction device, 6 ... Subject, 7 ... Strobe (flash) illumination device, 51 ... Image storage part, 52 ... Calculation unit, 53 ... correction coefficient recording unit

Claims (6)

An average luminance value of each frame of the video imaged with the first flash illumination is calculated, a correction coefficient of each frame is calculated from the average luminance value of each frame, and the first luminance after the imaging with the first flash illumination is calculated. A calculation unit that generates corrected image data using the image data of each frame of the video imaged by the flash illumination of 2 and the correction coefficient of each frame;
An image luminance automatic correction apparatus comprising: a correction coefficient recording unit that records the correction coefficient of each frame calculated by the calculation unit.   The calculation unit is configured to calculate the correction coefficient from the image data of each frame of the video shot with the first flash illumination, and use the second flash illumination after shooting with the first flash illumination. The correction coefficient of each frame is calculated from the average luminance value of each frame of the shot video, and corrected using the image data of each frame of the video shot with the first flash illumination and the correction coefficient of each frame The image brightness automatic correction device according to claim 1, which generates image data. The correction coefficient is a value proportional to [1 / average luminance value of each frame],
The image brightness automatic correction device according to claim 1, wherein the calculation unit generates corrected image data by multiplying the image data of each frame by the correction coefficient. The calculation unit calculates an average luminance value of each frame and an average luminance value of all frames, calculates a correction coefficient of each frame from the average luminance value of each frame and the average luminance value of all frames,
4. The image luminance automatic correction device according to claim 3, wherein the correction coefficient is [average luminance value of all frames / average luminance value of each frame].   5. The automatic image brightness correction device according to claim 1, wherein the arithmetic unit calculates an average brightness value of each frame by averaging brightness values of all pixels of each frame. 6.   A high-speed imaging device comprising the image brightness automatic correction device according to claim 1.

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